Vacuum brake booster

Abstract

To reduce the overall weight of a vacuum brake booster, the booster housing is provided with an axially extending central tube connecting the end walls of the housing in order to transmit the occurring axial forces. Two separate pistons are provided, a differential pressure piston surrounding the tube and a control valve piston disposed in the bore of the tube. Both pistons are connected with one another by radial pins extending through axial slots in the tube. The differential pressure piston is sealed by a diaphragm which progressively covers the slots when this piston moves in an operational direction. This arrangement reduces the axial length of the booster housing.

I claim: 
     
       1. A vacuum brake booster comprising: a housing having a longitudinal axis and two end walls transverse to said axis;   a tube disposed in said housing coaxial of said axis connected between said two end walls;   a movable wall disposed in said housing coaxial of said axis to divide said housing into a vacuum chamber and a working chamber;   a valve housing disposed within said tube containing therein a valve to control the pressure in said working chamber to generate a force proportional to the differential pressure in said vacuum and working chambers to act on said movable wall;   slots through the outer surface of said tube disposed in said vacuum chamber;   cross members extending through and guided in said slots to interconnect said valve housing and said movable wall on the vacuum side of said movable wall; and   said movable wall includes a diaphragm plate, a first rolling diaphragm disposed on one surface of said diaphragm plate disposed in said working chamber to provide a seal between said movable wall and said tube and at least one component disposed between said one surface and said first rolling diaphragm, said one component exerting an inwardly directed force on said first rolling diaphragm to cover said slots in a positively sealed relationship when said movable wall is displaced in an operative direction.   
     
     
       2. A booster according to claim 1, wherein: said tube includes a step in which said first rolling diaphragm is fastened.   
     
     
       3. A booster according to claim 1, wherein: said tube includes at least one inwardly extending projection to guide said valve housing therein.   
     
     
       4. A booster according to claim 1, wherein: said tube includes a radially inwardly extending projection to guide said valve housing therein, and   said valve housing includes a radially outwardly extending projection to guide said valve housing in said tube.   
     
     
       5. A booster according to claim 4, wherein: said projection of said valve housing is provided by the end of said valve housing in said tube having a larger diameter than the remainder of said valve housing.   
     
     
       6. A booster according to claim 5, wherein: a first annular chamber is formed between said valve housing and said tube adjacent said working chamber having one end thereof defined by said projection of said tube, and   a seal is disposed in said first annular chamber at said projection of said tube to seal said first annular chamber relative to said tube and said valve housing.   
     
     
       7. A booster according to claim 6, wherein: the other end of said first annular chamber is sealed by a second rolling diaphragm fastened between said tube and said valve housing.   
     
     
       8. A booster according to claim 7, wherein: an air filter is disposed in the end of said valve housing remote from said large diameter end, and   said second rolling diaphragm seals said air filter to said valve housing.   
     
     
       9. A booster according to claim 8, wherein: said first annular chamber is connected to said working chamber by at least one radial opening through the wall of said tube and to a second annular chamber inside said valve housing through a channel in a wall of said valve housing.   
     
     
       10. A booster according to claim 9, wherein: an inner chamber of said tube is connected to said vacuum chamber through said slots and to a third annular chamber inside said valve housing through an axial bore of said valve housing.   
     
     
       11. A booster according to claim 10, wherein: the outer surface of said valve housing is a sliding surface for said seal.   
     
     
       12. A booster according to claim 5, wherein: said cross members include pins screwed down through said one component of said movable wall and into said larger diameter end of said valve housing.   
     
     
       13. A booster according to claim 12, wherein: said one component of said movable wall includes a sheet member urging said movable wall against bushing, and   said pins hold said bushing and said sheet member together.   
     
     
       14. A booster according to claim 13, further including: a member disposed in the smaller diameter portion of said valve housing to add together a force generated by an actuating rod and said force generated by said differential pressure.   
     
     
       15. A booster according to claim 14, further including: a return spring disposed between one of said end walls remote from said valve housing and a spring plate abutting said bushing.   
     
     
       16. A booster according to claim 15, wherein: an end of said tube adjacent said one of said end walls includes therein fastening lugs to which a master brake cylinder can be fastened.   
     
     
       17. A brake booster having two booster units separated by a common wall arranged in tandem and according to claim 1, wherein: an outer wall of said housing encloses both of said two booster units and an inner portion of said outer wall forms a first tubular projection adjacent to and coaxial of said axis extending up to an end of said tube remote from said valve housing.   
     
     
       18. A booster according to claim 17, wherein: the additional one of said two booster units includes a second movable wall having on an inner portion thereof a second tubular projection adjacent to and coaxial of said axis and outside said tube held in position by said cross members.   
     
     
       19. A booster according to claim 18, wherein: said second tubular projection includes a bayonet catch for locking engagement into said cross members.   
     
     
       20. A booster according to claim 18, wherein: said common wall includes on an outer portion thereof a third tubular projection coaxial of and spaced from said axis which is connected to an end wall of said housing adjacent said valve housing.   
     
     
       21. A booster according to claim 20, further including: a return spring disposed between said common wall and a spring plate associated with said cross members.   
     
     
       22. A booster according to claim 21, wherein: a slide seal is disposed between the inner edge of said common wall and said second projection.   
     
     
       23. A booster according to claim 18, wherein: the diameter of said first projection is smaller than the diameter of said second projection.   
     
     
       24. A booster according to claim 23, wherein: a gap is provided between said first and second projections to connect the vacuum chambers of said two booster units together.   
     
     
       25. A booster according to claim 20, wherein: a gap is provided between said third projection and said outer wall to connect the working chambers of said two booster units together.